1. Field of the Invention
The present invention relates to the field of semiconductor test equipment, and more specifically to an apparatus for the fast and efficient transferring of integrated circuits between three locations: an input location, a test site location, and an output location where tested IC's are sorted according to test results.
2. Prior Art
Once fabricated, integrated circuits must undergo a plurality of tests to determine the circuits reliability and electrical characteristics. An apparatus such as the TES tri-temp SMD Handler model IPS-8990 is used in the prior art to transfer integrated circuit to and from a test location. Relevant parts of the apparatus are shown in FIG. 1.
Integrated circuits to be tested are stored in a tray 12. A pick and place assembly 14 loads a specified integrated circuit 13 from the input tray 12 and places it into the load slide 16. The loadslide then moves to the right and transfers the IC from the input chamber to the test chamber 18. Located in the test chamber 18 of the JLSI handler are three assemblies, a left pick and place assembly 20 and a middle pick and place assembly 22, and a work press assembly 24. The left pick and place assembly 20 moves integrated circuits from the load slide 16 to a turntable location 26 of turntable 28. A plurality (the exact number depends on the specific product) of integrated circuits may be stored in turntable 28 at any one time. Once an integrated circuit is loaded into turntable 28 at location 26, it is either heated or cooled so that testing may take place at an elevated or lowered temperature. The integrated circuit 13 is heated or cooled as it makes a revolution in turntable 28. Once the integrated circuit 13 has made a full revolution in turntable 28 and arrives once again at location 26, it is transferred by middle pick and place assembly 22 to test site location 30. At test site location 30 is a tester, such as a Trillium tester which conducts the actual electrical tests and characterization of the integrated circuit.
The middle pick and place assembly 22 only provides the integrated circuit to test site 30 from the turntable 28. Work press assembly 24 applies pressure to the integrated circuit 13 while it is being tested at test site location 30. Such pressure is necessary to carry out the test. Once testing is completed, work press assembly 24 transfers the integrated circuit 13 to the unload slide 32 where it is transferred from test chamber 18 and into storage area (output chamber) 34. In storage area 34 the integrated circuit is removed from the unload slide 32 by pick and place assembly 36 and placed into one of several storage bins 38. The integrated circuit is sorted depending upon its electrical characteristics. Once placed in the storage tray 38 the I.C. has completed its testing.
FIGS. 2(a-e) illustrate how integrated circuits are inefficiently transferred between locations in the test chamber by the prior art handler. FIG. 2a is a side view of test chamber 18 of the handler. Shown are the two pick and place assemblies 20 and 22 and the one work press assembly 24. It is important to note that the three assemblies 20, 22, and 24 are rigidly coupled to one another. Each of the assemblies is a fixed distance (four inches) from one another. The assemblies are fixed together as a single apparatus 42. The apparatus 42 resides in a single plane and slides in a horizontal direction on guide shaft 4. Also shown in FIG. 2a are the four IC locations within the test chamber 18 of the handler: the load slide 16 location, the turntable 26 location, the test site location 30, and unload slide 32 location. Each of these locations lie in a single plane and like the assemblies 20, 22, and 24 are spaced four inches apart from one another. Integrated circuits are moved by the assemblies 20, 22, and 24 between the locations in the test chamber 18.
FIG. 2a details the position of the assemblies at the start of a test cycle. At the start of the cycle it is assumed that the test pipeline is full of integrated circuits so that there is an integrated circuit at each of the four locations and the turntable has a full compliment of integrated circuits. At the start of the test cycle, work press assembly 24 has an integrated circuit A which has just completed testing in Trillium tester located at the test site 30. The middle pick and place assembly 22 has an integrated circuit B which has just completed a heating rotation in turntable 28, and the left pick and place assembly has an integrated circuit C from load slide 16.
During time T1 the entire apparatus 42 which includes assemblies 20, 22, and 24 slides over horizontally four inches as shown in FIG. 2b. In this way the left pick and place 20 holding integrated circuit C is positioned over the turntable at turntable location 26. Middle pick and place 22 holding integrated circuit B is positioned over test site location 30 and work press assembly 24 holding integrated circuit A is positioned over the unload slide 32.
During time T2 individual assemblies of the apparatus 42 move to the position illustrated in FIG. 2c. During time T2 the apparatus 42 remains in the position illustrated in FIG. 2b, however, the middle pick and place and the left pick and place change their respective positions in the vertical direction. The left pick and place 20 lengthens its shaft such that integrated circuit C can be placed at turntable location 26. Middle pick and place 22 lengthens its shaft so that untested integrated circuit B can be placed down into the test site well 30 for testing. The work press 24 places tested integrated circuit A into unload slide 32. Also during time T2, after the integrated circuits have been placed in their respective positions, each of the assemblies shortens its shaft length so that the apparatus 42 may slide on guide shaft 40 back four inches to its original position. It is important to note that integrated circuit B is not tested at this time. In order to test an integrated circuit the work press assembly 24 must be available to apply pressure to the integrated circuit during testing.
During time T3 the apparatus 42 slides back to the initial position as illustrated in FIG. 2d. While the apparatus 42 slides from the second position four inches back to the initial position, neither the pick and place assemblies 20 and 22 nor the work press assembly 24 is carrying an integrated circuit. Also during T3 turntable 28 rotates one position so that a new integrated circuit C', which has undergone heat treatment, is now available at turntable location 26. Also at this time, a new integrated circuit, circuit D, moves on load slide 16 from the input chamber to the test chamber 18.
During time T4 integrated circuit B is finally tested as illustrated in FIG. 2e. At the beginning of time T4 each of the shafts of the assemblies lengthen. The left pick and place 20 lengthens to pick integrated circuit D which recently moved into the test area on load slide 16. The middle pick and place 22 lengthens its shaft to pick up integrated circuit C' which has recently completed its heat or cold treatment rotation in turntable 28. The work press 24 lengthens its shaft so that it can apply pressure to integrated circuit B while it is being tested by the Trillium tester at the test site location 30. The work press assembly 24 applies pressure to integrated circuit B during the entire course of testing. The actual testing time can vary in length depending upon the complexity of the integrated circuit and the types of tests conducted. During the entire test time, the apparatus 42 remains in the horizontal position as shown in FIG. 2e. During testing pick and place assemblies shorten their respective shafts to the up position. Once testing of integrated circuit B has completed, work press assembly 24 shortens its shaft. The apparatus is now back to the position as shown in FIG. 2a. The test cycle is complete at this time.
Integrated circuits continue to be serially manipulated in the above fashion. The total time required for a single test cycle is Ttotal=T1+T2+T3+T4. The total test handler cycle time can be broken into two parts, the index time and the actual test time. The index time is the time required to transfer parts between the different locations while the Trillium tester is not testing integrated circuits (i.e. the time from the end of the test to start of test). In the prior art the index time is (T1+T2+T3+T4-the test time) which is approximately 3.2 seconds. The actual test time of an integrated circuit for a part varies from 2 to 20 seconds depending upon the types of tests and the complexity of the circuit. Unfortunately, during the index time of the test cycle the testing apparatus (trillium tester) sits idle.
Testing machines, such as Trillium testers, are extremely expensive. It is, therefore, beneficial to reduce the index time of handlers as much as possible so that expensive testing machines may be utilized more efficiently.
Thus what is needed is a method and apparatus to efficiently transfer integrated circuits to and from a tester so that the tester can spend more time testing and less time sitting idle.